Many studies have shown that the consumption of a low glycemic index (LGI) meal before exercise promotes lipid oxidation, thus lowering the amount of hypoglycemic occurrence and improving physical performance. However, other studies have not observed such benefits. The objective of this study is to demonstrate the impact of ingesting various glycemic index (GI) breakfasts on the endurance performance of high-level cyclists. Ten men completed three randomly allocated protocols, and each was separated by a time interval of a minimum of seven days. Each protocol was composed of a time trial, where a measure was taken three hours either after consuming a breakfast of low or high glycemic index containing three grams of glucose per kg of body weight, or after completing exercise while fasting.
The race time results demonstrated that there were no significant differences between the protocols. However, the number of revolutions per minutes (RPM) was significantly higher with the high glycemic index level protocol (94,3 ± 9,9) in comparison to the fasting protocol (87,7 ± 8,9) (p<0,005). Furthermore, the capillary glycemic profile showed that, during exercise at 30 minutes, blood glucose level was significantly higher in the fasting protocol (5,47 ± 0,76 mmol/L) in comparison to the high glycemic index (HGI) protocol (4,99 ± 0,91 mmol/L) (p<0,002).
Our study did not confirm that the consumption of a LGI meal before physical exercise significantly improves physical performance. Yet it demonstrated that the diversity of protocols used to evaluate the impact of glycemic index on physical performance could generate positive impact during the race time. Therefore, there is a need to conduct further research that can reproduce athletic competition situations, such as time trials.